mysql - 事件记录 : Delete duplicate records

Question

如果在特定日期有多个记录，我想删除当天除最新记录外的所有记录。例如，在下表中，id 为 9、10、12 的记录具有相同的日期。因此，应删除 9 和 10，因为 ID 为 12 的记录具有最新日期。

id      date
1   2012-04-25 00:00:00.000000
2   2012-04-26 00:00:00.000000
3   2012-04-23 00:00:00.000000
4   2012-04-24 00:00:00.000000
5   2012-05-01 00:00:00.000000
6   2012-05-02 00:00:00.000000
7   2012-05-03 00:00:00.000000
8   2012-05-04 00:00:00.000000
9   2012-04-30 00:30:00.000000
10  2012-04-30 18:00:00.000000
11  2012-04-29 00:00:00.000000
12  2012-04-30 18:40:00.000000
13  2012-05-05 00:00:00.000000
14  2012-05-05 09:31:31.000000

这是删除重复项的(脏)rake 任务

task :remove_duplicate do
  Rake::Task["remove_duplicate"].invoke
end

task :remove_duplicate => :environment do
  weights = Weight.count(:group => "DATE(date)", :having => "COUNT(id) > 1")
  weights_to_delete = []
  weights.each do |weight|

    start_date = weight[0].to_date.beginning_of_day
    end_date = weight[0].to_date.end_of_day
    day_weights = Weight.where("date >= ? and date <= ?", start_date, end_date).order(:date)
    day_weights[0..-2].each do |weight|
      weights_to_delete.push weight.id
    end
  end
  Weight.delete(weights_to_delete)
end

虽然我能够按照我解释的那样删除记录，但我对我采用的方法并不满意。请指导我删除特定日期的重复记录，只保留最新的记录，更好地利用 ActiveRecord API。

谢谢，阿米特·帕特尔

Answer 1

此方法可能会很慢，所以我不推荐它，除非您定期运行它。

Weight.all.each do |weight|
  Weight.order("id desc").where(date: weight.date).all.drop(1).each { |w| w.delete }
end